(1.) Field of the Invention
The present invention relates to an electrolytic capacitor (electric condenser). More particularly, the present invention relates to an electrolytic capacitor which is capable of discharging hydrogen gas electrolytically generated in the capacitor to prevent an undesirable increase in pressure in the capacitor, and thus has an improved safety and an enhanced durability.
(2.) Description of the Related Art
It is known that a conventional electrolytic capacitor comprises a closed container; an electrolytic liquid; at least one pair of an anode foil and a cathode foil immersed in the electrolytic liquid, alternately superimposed on each other and coiled together, the alternately superimposed anode foil and cathode foil being spaced apart by at least one insulating spacer, to provide an electrolytic capacitor element; and an anode terminal and a cathode terminal respectively connected to the anode foil and the cathode foil and extending to the outside of the container.
Also, it is known that, when the conventional electrolytic capacitor is used at a high temperature of, for example, 85.degree. C. or more under a load, a leak current is generated due to oxide layers formed on the anode foil. This leak current causes the electrolytic liquid to be electrolytically decomposed, and to produce a decomposition gas consisting essentially of hydrogen gas.
The generation of the decomposition gas results in an increase in pressure in the container and, finally, in a rupture of the container due to the increased pressure therein.
In order to eliminate the above-mentioned disadvantages, an attempt has been made to add a hydrogen gas-absorbing agent into the electrolytic liquid or to give the oxide layer on the anode foil an excessive thickness to decrease the generation of the leak current. Also, an attempt has been made to form a portion of the container of a porous ceramic material to allow hydrogen gas generated in the container to permeate therethrough to the outside of the container.
Furthermore, an attempt has been made to provide a weak (thin) point in a sealing top or lid portion of the container so that, when a pressure of the hydrogen gas generated in the container increases to a predetermined level, the container is easily opened or broken at the weak portion thereof and the detrimental influence on the environment around the capacitor due to the rupture of the container is reduced as much as possible.
However, the above-mentioned attempts are not always satisfactory for eliminating the disadvantages of the conventional electrolytic capacitor, since they sometimes generate other disadvantages.